In electrophotographic processes or electrostatic recording process, developers which visualize electrostatic images or electrostatic latent images are classified into two-component developers formed of toner and carrier particles and one-component developers which are substantially formed of only toner, that is, which do not use carrier particles. The one-component developers may be classified into magnetic one-component developers which contain a magnetic component, and nonmagnetic one-component developers which do not contain a magnetic component. Fluiding agents such as colloidal silica, may be often independently added to nonmagnetic one-component developers to improve the fluidity of toner. In general, coloring particles obtained by dispersing a colorant such as carbon black or other additives in a latex are used as the toner.
Toners may be prepared using a pulverizing method or a polymerizing method. In the pulverizing method, a synthesized resin, a colorant, and when required, other additives are melted, pulverized, and then sorted to obtain particles having desirable diameters, to thereby obtain the toner. In the polymerizing method, a colorant, a polymerization initiator, and when required, other additives such as a crosslinking agent or an antistatic agent, are uniformly dissolved in or dispersed into a polymerizable monomer to prepare a polymerizable monomer composition. Then, the polymerizable monomer composition is dispersed into an aqueous dispersion medium, including a dispersion stabilizer, using a stirrer to form micro droplet particles of the polymerizable monomer composition. Subsequently, the temperature is increased and then a suspension polymerization process is performed to obtain colored polymerization particles having desirable diameters, that is, a polymerization toner.
In image forming apparatuses such as electrophotographic apparatuses or electrostatic recording apparatuses, an image is formed by exposing an image on a uniformly charged photoreceptor to form an electrostatic latent image; attaching toner to the electrostatic latent image to transfer the toner image onto a transfer medium such as a transfer paper or the like; and then fusing the toner image on the transfer medium using any of a variety of methods including heating, pressurizing, applying a solvent vapor, and the like. In most fusing processes, the transfer medium with the toner image passes through fusing rollers and pressing rollers, and the toner is heated and pressed to fuse the toner image to the transfer medium.
Images formed by an image forming apparatus such as an electrophotocopier should satisfy the requirements of high precision and accuracy. Conventionally, toner used in an image forming apparatus is usually obtained using a pulverizing method. According to the pulverizing method, coloring particles having a large range of sizes are formed. Thus, to obtain satisfactory developing properties, there is a need to sort the coloring particles obtained through pulverization according to size so as to reduce the particle size distribution of toner. However, it is difficult to precisely control the particle size and the particle size distribution of the toner using a conventional mixing/pulverizing process in the manufacture of toner suitable for an electrophotographic process or an electrostatic recording process. Also, when preparing a fine-particle toner, the toner preparation yield is adversely affected by the sorting process. In addition, there are limits to the change/adjustment of toner design for obtaining desirable charging and fusing properties. Accordingly, a polymerized toner, the size of particles of which is easy to control and which do not need to undergo a complex manufacturing process such as sorting, has been highlighted recently.
When toner is prepared using a polymerizing method, a polymerized toner having a desired particle size and particle size distribution may be obtained without pulverizing or sorting.
However, although such a polymerized toner can be used to secure adequate printing performance and image quality when printing, functional properties such as fusibility and durability of the toner need be also considered. Thus, it is desirable to develop toner having optimized rheological properties.